The aim is to address issues in the policy and practice of treating hypertension, particularly "mild" hypertension. In 1973-1974 the Hypertension Detection and Follow-up Program (HDFP) carried out a population based screen of over 159,000 persons, ages 30-69 years, in 14 U.S. communities; 10940 men and women, including both blacks and whites were enrolled in the trial and followed for mortality and morbidity through 1979. A number of issues of interest to medical scientists and clinicians will be addressed by analyses of the extensive database of the HDFP and by an extension of mortality surveillance to 10 years. Hypertension remains one of the most common adult chronic diseases, affecting perhaps 35 million Americans. Although data from both observational and experimental studies support the view that mild hypertension is a very significant part of the public health problem of high blood pressure, the issue of how to treat mild hypertension remains controversial. It is not an inconsequential academic controversy. Before deciding whether to treat patients with mild hypertension, perhaps for the rest of their lives, a clinician must weight the largely unknown risks associated with long-term exposure to high blood pressure. The potential benefit of antihypertensive drug treatment when both mortality and morbidity are considered will be examined in HDFP hypertensive participants. Evidence of long-term, adverse effects of this treatment will be studied, particularly for problems which could not be medically managed effectively. Factors which were predictive of cardiovascular endpoints or which differentiated treatment response will be identified and studied both for their impact on treatment effects in various subgroups and for insights into approaches to treatment. These investigations can shed important light on the benefits and risks of treatment in individuals with various characteristics.